The present invention generally relates to a system for providing data services to a circuit switched exchange and, in particular, relates to such a system having a data services adjunct serially interconnected with an existing voice communication path.
The recent development of data oriented devices has impacted substantially every business, regardless of its size. However, the efficient integration and use of such devices have yet to be fully realized. One reason is that the maximum use of such data devices and services requires the full interconnectivity and access thereto by all subscribers to such a related system. For example, in an envisioned electronic office the accounting department would need full interconnectivity with inventory records, sales, and etc. and management would need full interconnectivity to productivity, inventory and other manufacturing information.
Ultimately, a fully integrated voice/data network is anticipated not only for local offices but for entire communication networks. Perhaps one primary reason for such integration is that during a telephone call the actual information conveyed is comparatively quite small with respect to a data system over the same time period. Further, a data network is characterized in that the data transmissions are most frequently in the form of relatively short bursts of high data rate information. Hence, the use of a single pair of wires as they presently exist for telephonic services is not unreasonably considered as a path for integrated voice/data services.
Perhaps the largest impediment to such a full voice/data integrated network is the fact that most telephonic services are provided by what is generally referred to as circuit switched exchanges. As used herein the phrase "circuit switched exchange" is intended to include all analog exchanges and all non-packet digital exchanges. The essential characteristic of circuit switched exchanges that is a detriment to the use thereof for data services is that a circuit switched exchange sets up a path across a network prior to the initiation of any communication i.e. conversation, and maintains that same path during the entire conversation, thereby locking out the use of that path from others. Further, such a path is removed only after all information has been communicated. As well known, during any conventional telephone conversation there exists many periods of time when the line is not actually conveying information but during which time no other party can access that line to transmit data. Naturally, in a integrated voice/data network these intervals could be used to transmit bursts of data to a data peripheral connected via the same twisted pair of wires. As a consequence, a circuit switched exchange, in the presence of an integrated voice/data system, would necessarily be obsolete and need to be replaced by, for example, a digital switching exchange.
As it happens the majority of businesses that are presently considering full utilization of data services most likely own a circuit switched exchange, frequently known as a private automatic business exchange (PABX). In addition, present trends indicate that data services are usually provided, in the evolutionary sense, at least initially, to a relatively small number of offices or personnel. This is generally accomplished on a line-by-line basis by means of what has become commonly known as a modem link. Quite obviously such a scheme can become extremely expensive and can only provide limited services as more and more offices and personnel are provided with full data services. In addition, data transmissions via such a modem must still use the circuit switched exchanges and are thus subject to the path management difficulties associated therewith.
At the present time the primary alternative to the extensive use of modems is the installation of a local area network (LAN). A local area network usually requires a separate digital switching system as well as the wiring of the entire building to be provided with data services. Consequently, companies presently seeking to grow into full electronic offices are faced with three choices, i.e. the massive use of modems, the use of a LAN, or the removal of the present circuit switched exchange and installation of a fully integrated voice/data switch. As a consequence, many businesses feel forced into expensive and inappropriate compromises in many data services areas and often must give up a circuit switched exchange that has many useful years remaining.